FIG. 20 shows a position control drive apparatus disclosed in U.S. Pat. Nos. 3,902,084 and 3,902,085 and known as an inch worm. The drive apparatus shown in FIG. 20 has three tubular piezoelectric elements 1, 2, and 3 and a shaft 4. When a control voltage is applied, the piezoelectric elements 1 and 3 are deformed to be fixed by the shaft 4 and the piezoelectric element 2 is deformed to extend along the axial direction of the shaft 4. With this arrangement, when the phases of the AC voltages applied to the piezoelectric elements 1, 2, and 3 are appropriately shifted from each other, the shaft 4 can be displaced relative to the piezoelectric elements 1, 2, and 3. When such an apparatus is used, position control on the order of submicrons can be performed. The step size can be changed in accordance with the voltages to be applied, and the moving speed reaches as high as 0.2 mm/sec.
With the arrangement of FIG. 20, however, since friction is utilized, abrasion, slippage, and play can occur. Therefore, it is difficult to perform precise position control and to maintain reliability.
Another apparatus is reported wherein clamping is performed utilizing electromagnets in place of the piezoelectric elements 1 and 3 shown in FIG. 20. In this case, however, heat generated by the coils of the electromagnets degrades the position control precision.
Furthermore, a stepping motor is widely used for such precise position control. In this case, however, heat generated by the coil of the stepping motor degrades the position control precision. If a gear is utilized to decrease the step size, a backlash occurs.
The present applicant previously proposed a so-called relay-type piezoelectric motor in Japanese Unexamined Patent Publication Nos. 61-185078 and 61-185079. According to this relay-type piezoelectric motor, a plurality of piezoelectric actuators are vibrated by voltages having a plurality of phases, and the vibration is transmitted to a moving part (or a rotor) through magnetic coupling. The arrangement of the actuators and the moving part and the phase of the drive signal are set such that the coupling of the actuator and the moving part is maximum in a phase in which the vibrating direction of the actuator coincides with the moving direction of the moving part. The actuators are sequentially coupled with the moving part with the maximum coupling degree and drive the moving part in a predetermined direction. However, when bimorph actuators are used as the piezoelectric actuators, as in this case, the drive force is small and thus the application is limited.
When two- or three-dimensional positioning is performed utilizing the apparatus as shown in FIG. 20, and particularly when a desired position is to be obtained in a trial-and-error manner, positioning generally takes time. Also, drive apparatuses must be separately provided for X, Y, and Z directions, resulting in a complex, expensive control system.
The present invention has been made in consideration of the above situation and has as its object to provide a drive apparatus which can perform fine driving along a desired curve with a simple arrangement.
It is another object of the present invention to provide a drive apparatus which can perform fine driving with a simple arrangement, which can perform driving with both a synchronous motor and an induction motor, and which has a wide application range.
It is still another object of the present invention to provide a high-resolution, high-reliability motor unit which can perform more precise positioning by utilizing such a drive apparatus.
It is still another object of the present invention to increase the drive force of a motor unit of this type.